The present invention generally relates to rotary wood chippers and specifically relates to chip separators used with rotary wood chippers.
Rotary wood chippers are large, heavy machines and are commonly built with an integrated trailer towing frame for portability to a job site. An infeed chute with a powered conveyor is often provided for feeding material, typically a tree, into the front side of a cutter disk.
The cutter disk is the heart of a wood chipper and is typically a thick metal disk with at least a pair of cutter knives which are mounted adjacent chip slots in the disk. The disk is rotated at relatively high speed and is typically mounted in a cylindrical chamber and at an acute angle to the direction of feed, such that the knives tend to draw the material into the disk. As the material is fed into the front side of the disk, the knives continuously slice the end of the material to form chips which pass through the chip slots to the back of the disk. The chips are removed from the back of the disk in part by centripetal force. Fan blades which are typically mounted on the back of the disk induce an airflow which also removes the chips from the back of the disk and which carries the chips through a tangential chip chute for discharge from the chipper. Such wood chippers typically have an internal combustion engine, also mounted on the integrated frame, to power the cutter disk and the infeed conveyor.
Some materials, such as grit, leaves, needles and small branches, are not cut and remain on the front side of the disk where they are discarded as chaff. Because of the forces generated at the back of the disk, chips are frequently forced past the edge of the disk to the front of the disk, where they are discarded with the chaff which is costly to the chipper operator.
While attempts have previously been made in trying to minimize the crossover of chips and their loss by discard with chaff, these attempts have proven expensive, ineffective or otherwise impractical. One approach has been to use a divider bar circumscribing the perimeter of the disk to block the passage of chips past the disk edge. The divider bar is basically a flat bar bent edgewise into a ring and mounted in the cutter disk chamber to the chamber wall which circumscribes the cutter disk. The divider bar projects into the chamber and is positioned adjacent the back of the disk. A notch can be ground into the back of the disk, near its perimeter and circumscribing the disk, such that the bar will be fit into the notch. Another approach uses a divider bar and a groove circumscribing the perimeter of the disk to close off the passage of chips around the edge of the disk. This is similar to the above approach except that a groove is ground into the edge of the disk, circumscribing the disk, and the divider bar projects into this groove. These attempts have commonly focused upon closing the gap between the perimeter edge of the cutter disk and the adjoining wall of the chamber in which the disk is mounted. However, chips still pass around the disk edge to the front side in spite of these attempts to minimize this occurrence. Further, such structures require close manufacturing tolerances. While the required tolerances can be acquired during manufacturing, but at a significant cost, wear from the rugged duty encountered by these machines quickly degrades these tolerances and frequent adjustments and alignments are required. Further, such systems require expensive installation procedures as well as frequent and therefore costly maintenance.